1. Field of the Invention
The present invention relates to a thermal printer provided with a platen roller unit and a thermal head unit, and more specifically to a support structure for a thermal head unit.
2. Background Information
One example of a conventional thermal printer provided with a platen roller and a thermal head is shown in FIGS. 4A, 4B and 5. The thermal printer has a platen roller 20 rotatably mounted on a frame 22 in the width direction of a sheet of recording medium (not shown). A thermal head 24 is fixedly supported by a head unit 26 and is in facing relationship with the platen roller 20 and arranged so as to come into pressing contact with the platen roller 20. The thermal head 24 is provided with a pressure member which is integrally attached to the rear surface of the thermal head 24 through screws or the like and which causes the thermal head 24 to come into pressing contact with the platen roller 20.
The pressure member comprises a resilient member 28 and a head unit pressure plate 30 which are arranged such that the resilient member 28 is interposed between the head unit pressure plate 30 and the head unit 26 so that the pressure member expands and contracts elastically within a predetermined clearance between the two. As a result, when the thermal head 24 is assembled in a predetermined position in the frame 22 of the thermal printer together with the pressure member, the thermal head 24 contacts the platen roller 20 with a predetermined pressure contacting force (FIG. 4B).
In the conventional thermal printer shown in FIGS. 4A, 4B and 5, the thermal head 24 is integrally supported by the head unit pressure plate 30 of the pressure member through the head unit 26, and when the thermal head 24 is brought into pressure contact with the platen roller 20 by the action of the resilient member 28 of the pressure member, the resilient member 28 applies a uniform energizing force to the thermal head 24 so as to absorb a one-sided or biased contact.
However, in the conventional thermal printer shown in FIGS. 4A, 4B and 5, the pressure member and the thermal head 24 are integrated and the pressure member is fixedly supported at one end thereof to the frame 22 by fixing means such as screws 32. Thus maintenance and replacement of the thermal head 24 becomes more complicated and time consuming since the pressure member and the thermal head 24 are not independent of each other and removal of the fixing means 32 becomes necessary. Furthermore, tools are often required to provide a large opening at the pressure contact portion between the platen roller 20 and the thermal head 24 during replacement of the thermal head 24 or removal of a paper jam, thereby causing drawbacks that maintenance of the thermal printer and replacement of components are laborious and time-consuming.